Vitamin B12

Vitamin B12

Description

Cobalamin, also known as B12, is a member of the water-soluble family of B vitamins. It is a key factor in the body's proper use of iron and formation of red blood cells. The nervous system also relies on an adequate supply of cobalamin to function appropriately, as it is an essential component in the creation and maintenance of the myelin sheath that lines nerve cells. Other roles of cobalamin include working with pyridoxine (vitamin B6 and folic acid to reduce harmful homocysteine levels, participating in the metabolization of food, and keeping the immune system operating smoothly.

General use

Very small amounts of cobalamin are needed to maintain good health. The RDA value is 0.3 micrograms (mcg) for infants under 6 months, 0.5 mcg for those 6 months to 1 year old, 0.7 mcg for children 1-3 years old, 1.0 mcg for children 4-6 years old, 1.4 mcg for children 7-10 years old, and 2 mcg for those 11 years of age and older. Requirements are slightly higher for pregnant (2.2 mcg) and lactating (2.6 mcg) women.

The primary conditions that benefit from supplementation with cobalamin are megaloblastic and pernicious anemia . Megaloblastic anemia is a state resulting from an inadequate intake of cobalamin, to which vegans are particularly susceptible because of the lack of animal food sources. Vegans, who do not consume any animal products including meat, dairy, or eggs, should take at least 2 mcg of cobalamin per day in order to prevent this condition. In the case of pernicious anemia, intake may be appropriate but absorption is poor due to a lack of normal stomach substance, called intrinsic factor, that facilitates absorption of vitamin B12. Large doses are required to treat pernicious anemia, which occurs most commonly in the elderly population as a result of decreased production of intrinsic factor by the stomach. Supplements are generally effective when taken orally in very large amounts (300-1000 mcg/day) even if no intrinsic factor is produced. These supplements require a prescription, and should be administered with the guidance of a health care provider. Injections, instead of the supplements, are often used.

Those who have infections, burns , some types of cancer , recent surgery, illnesses that cause decay or loss of strength, or high amounts of stress may need more than the RDA amount of B12 and other B vitamins. A balanced supplement is the best approach.

Male infertility can sometimes be resolved through use of cobalamin supplements. Other conditions that may be improved by cobalamin supplementation include: asthma, atherosclerosis (hardening of the arteries caused by plaque formation in the arteries), bursitis (inflammation of a bodily pouch, especially the shoulder or elbow), Crohn's disease (chronic recurrent inflammation of the intestines), depression , diabetes, high cholesterol, osteoporosis , and vitiligo (milky-white patches on the skin). There is not enough evidence to judge whether supplementation for these diseases is effective.

Preparations

Natural sources

Usable cobalamin is only found naturally in animal source foods. Fresh food is best, as freezing and exposure to light may destroy some of the vitamin content. Clams and beef liver have very high cobalamin levels. Other good sources include chicken liver, beef, lamb, tuna, flounder, liverwurst, eggs, and dairy products. Some plant foods may contain cobalamin, but it is not in a form that is usable by the body.

Supplemental sources

Cobalamin supplements are available in both oral and injectable formulations. A nasal gel is also made. Generally a balanced B-complex vitamin is preferable to taking high doses of cobalamin unless there is a specific indication for it, such as megaloblastic anemia. Strict vegetarians will need to incorporate a supplemental source of B12 in the diet. Cyanocobalamin is the form most commonly available in supplements. Two other, possibly more effective, types are hydrocobalamin and methyl-cobalamin. As with all supplements, cobalamin should be stored in a cool, dry, dark place and out of the reach of children.

Deficiency

Cobalamin deficiency may be manifested as a variety of symptoms since cobalamin is so widely used in the body. Severe fatigue may occur initially. Effects on the nervous system can be wide-ranging, and include weakness, numbness and tingling of the limbs, memory loss , confusion, delusion, poor balance and reflexes, hearing difficulties, and even dementia . Severe deficiency may appear similar to multiple sclerosis . Nausea and diarrhea are possible gastrointestinal signs. The anemia that results from prolonged deficiency may also be seen as a pallor, especially in mucous membranes such as the gums and the lining of the inner surface of the eye.

Megaloblastic anemia is a common result of inadequate cobalamin. This condition can also result if a person stops secreting enough intrinsic factor in the stomach, a substance essential for the absorption of cobalamin. Inadequate intrinsic factor leads to pernicious anemia, so called because it persists despite iron supplementation. Long-term deficiencies of cobalamin also allow homocysteine levels to build up. Negative effects of large amounts of circulating homocysteine include heart disease , and possibly brain toxicity. Taking high levels of folic acid supplements can mask cobalamin deficiency and prevent the development of megaloblastic anemia, but neurological damage can still occur. This damage may become permanent if the cobalamin deficiency persists for a long period of time.

Risk factors for deficiency

The primary groups at risk for cobalamin deficiency are vegans who are not taking supplements, and the elderly. Older adults are more likely to have both insufficient intrinsic factor secreted by the stomach and low levels of stomach acid, causing cobalamin to be poorly absorbed. Malabsorptive diseases and stomach surgery can also predispose to a deficiency.

Precautions

People who are sensitive to cobalamin or cobalt should not take cobalamin supplements. Symptoms of hypersensitivity may include swelling, itching , and shock. Adverse effects resulting from B12 supplementation are rare. Cobalamin should also be avoided by those who have a type of hereditary optic nerve atrophy known as Leber's disease.

Side effects

Very high doses of cobalamin may sometimes cause acne .

Interactions

Large amounts of vitamin C taken within an hour of vitamin B supplements will destroy the cobalamin component. Absorption of cobalamin is also impaired by deficiencies of folic acid, iron, or vitamin E . Improved absorption occurs when it is taken with other B vitamins or calcium . Some medications may also cause an increased use or decreased absorption of this vitamin. Those on colchicine, corticosteroids, methotrexate, metformin, phenformin, oral contraceptives, cholestyramine, colestipol, clofibrate, epoetin, neomycin, or supplemental potassium may need extra cobalamin. Use of nicotine products or excessive alcohol can deplete B12.

Vitamin B12

Medical Discoveries
COPYRIGHT 1997 Thomson Gale

Vitamin B12

Vitamin B12 was discovered simultaneously by two research teams, one in the United States and one in England. It was the culmination of an intensive worldwide search for a compound that could effectively treat pernicious anemia.

B12 and Liver

During the 1930s, researchers around the world began trying to isolate the active ingredient in liver that contained its curative properties. The "antipernicious anemia factor" was believed to be a B vitamin. It was even given the name B12 long before it was isolated.

Testing was surprisingly slow. Patients were fed extracts of liver rather than the liver itself, but for some reason researchers could not measure the amount of vitamin B12 these liver extracts contained. They could only guess at the extracts' potency by measuring red blood cell growth in each patient's blood.

For years, Karl Folkers, an American chemist at a prominent pharmaceutical company, had been directing a research team that was working on the problem. In 1948, the group finally came up with a solution. They found they could measure the vitamin indirectly by measuring the growth rate of certain bacteria that needed vitamin B12 to grow. This system speeded the purification process of the vitamin enormously.

The New Vitamin

The new vitamin was a large and complicated molecule roughly four times the size of a penicillin molecule. The molecule was so complex that its structure could only be worked out through the aid of advanced technology. In 1956 English physicist Dorothy Hodgkin (1910-) completed the mapping of B12′s chemical structure by using x-ray crystallography. She received the 1964 Nobel Prize in chemistry for her work. Vitamin B12 was finally synthesized by Robert Burns Woodward (1917-1979) in 1971, after a ten-year effort.

Pernicious Anemia

Pernicious anemia is a blood disorder in which red blood cells fail to develop normally. The steady decline of red blood corpuscles eventually leads to death. The disease was first described completely in 1849 by English physician Thomas Addison (1793-1860). Addison noted the typical symptoms included increasing weakness and pallor of the patient. This was accompanied by obesity (weight gain) rather than weight loss.

Until the 1920s, this pernicious anemia was always fatal. Then two physicians named George Richards Minot (1885-1950) and William Perry Murphy became inspired by George Whipple's (1878-1976) studies. The Whipple studies showed that beef liver could improve the formation of red corpuscles in anemic dogs. To test Whipple's findings, Minot and Perry began feeding their patients large amounts of beef liver. In 1926, the researchers were able to announce that a daily diet of about a half a pound of liver could control the disease. For their work, Minot, Murphy, and Whipple shared the 1934 Nobel Prize in medicine.

The isolation and synthesis of B12 removed pernicious anemia from the list of deadly medical problems. B12 was the last vitamin to be discovered.
Work on the vitamin served to round out the remarkable half-century of vitamin research that began in the 1890s with Dutch physician Christiaan Eijkman (1858-1930).

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vitamin B12

vitamin B12 A cobalt‐containing compound, cobalamin, essential for normal metabolism of folic acid, and hence for cell division. Deficiency leads to pernicious anaemia when immature red blood cell precursors are released into the bloodstream, and there is degeneration of the spinal cord. The absorption of vitamin B12 requires a specific protein (intrinsic factor) which is secreted in the gastric juice and it is failure of absorption, rather than dietary deficiency, that is the more usual cause of the problem. However, B12 is found only in animal foods so vegans have to rely on bacterial preparations.

Meat, eggs, and dairy produce are rich sources and dietary deficiency is unlikely except among vegans.

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